A dimmer is a device that can change light emissions from lamps by changing the lamp's power consumption. Some lamps, such as fluorescent lamps, do not have commercial dimmers, and thus; their power consumption and brightness remains relatively constant. Other lamps, such as incandescent lamps, can be dimmed by simple dimmer circuitry.
The main component of these dimmers (often a Silicon-Controlled Rectifier (i.e., SCR) or a Triode for Alternating Current (i.e., TRIAC)) is activated by a resistance that is set by a resistor (such as a variable resistor) to produce a periodical current suppression in a portion of the AC power cycles. This periodical current suppression induces a reduction in power-supply to the filament of the incandescent lamps, thus reducing the incandescent lamp light (i.e., thermal) power and thus reducing the lamp brightness.
The filament temperature is reduced due to the reduced heating power caused by activation of the dimmer. The filament's blackbody radiation power (hence the light emission) is very sensitive to its temperature. Every incandescent lamp is designed to optimize against this temperature parameter. Small deviation from its optimum condition would cause great reduction in light emission. Therefore, a small reduction of power consumption in the incandescent lamp would cause a disproportionately greater reduction in brightness. In other words, these dimmers typically reduce the brightness of the incandescent lamp proportionally much more than the reduction of power consumption. For instance, some dimmers could reduce the brightness to 10% of the original level by reducing only 10% of original power consumption. Thus, 90% of power usage produces only 10% of the brightness, as compared to having 100% of the power usage. This is not a desirable property from an energy saving point of view.
Commercial dimmable LED lamps are typically fabricated with Pulse Width Modulation (PWM) and/or TRIAC subsystems. The dimmable LED lamps may also consist of some more subsystems, including 1) an energy source, such as power supply or battery; 2) the LED lighting subsystem consisting of at least one LED; and 3) a constant current (or voltage) drive Integrated Circuits (IC) that regulates the supplied current (voltage) into the LED lighting subsystem. The power supply may be combined with the PWM (or TRIAC) module to become a PWM (or TRIAC) modified power supply.
The PWM subsystem modifies the input power into a form of periodic pulsed current with regulated duty factor. The level of the regulated duty factor causes a corresponding (so-called, “effective”) current-level input into the LED lighting subsystem. This current-level (and thus the duty factor of this pulsed current) causes the LED lighting subsystem to produce corresponding light emission levels. The duty factor of the PWM is controlled by circuitry that includes a variable resistor that has a tunable resistance controlled by a knob or other control. To dim the LED lamp, one can use the knob to tune the variable resistor to adjust the duty factor of the PWM resulting in a desired lighting level thereby effectuating the desired dimming operation. The TRIAC performs the periodic input current suppression as described in previous paragraph regulating the “effective” input power as well.
As stated, the commercial designs of dimmable LED lamps all incorporate sophisticated PWM circuitry or TRIACs; regulate the power level supplies into the lamps. In short, these dimmers choke the power (from the supply-side) to a regulated level; and then deliver the power to the lighting subsystems (or the so-called light-bulbs) at regulated levels without altering any part of the LED lighting subsystems, the “light-bulbs”. Thus, we categorize these dimmers as “supply-side initiated dimmers”, or the “supply-side dimmers” in this patent disclosure. This term, the “supply-side dimmer” is named in contrast to the “demand-side initiated dimmer”, or the “demand-side dimmer”, which is the inventive concept described in detail hereinafter.